The invention relates to an extruder arrangement 1 for viscous material, especially rubber or synthetic rubber mixtures, and includes a screw extruder having an extruder screw which is followed, on the downstream side when viewed in the direction of conveyance, by a conveying device.
Such an extruder arrangement is known from EP-A1-508 079. With this approach, an extruder is combined with a geared pump. Geared pumps are more resistant to pressure than are screw extruders. In addition, the output of a gear pump is considerably better, so that the material that is to be conveyed can have a lower temperature. Furthermore, the vibrations of the geared pump that are introduced through the screw walls into the material that is to be extruded are dampened.
However, a geared pump has the drawback that leakage streams result to a certain extent that require a separate sealing. A geared pump must be manufactured very precisely, which makes the manufacture more expensive.
It has furthermore already been proposed to construct a pump in the manner of a planetary gearing. For the sake of simplicity, such a pump will here be signified as a planetary pump. With this approach, the sun or central gear can be connected directly with the extruder screw of the screw extruder, so that there is no need for a separate mounting of the end of the screw. Rather, the support of the end of the screw can be provided on the downstream side of the planetary pump.
A drawback of this approach is that the conveying properties of elastomeric materials such as rubber or rubber mixtures for the tire industry are greatly dependent upon differing parameters. If due to the prevailing viscosity of the material the planetary pump must be advanced to a greater extent than the extruder screw, an underpressure or partial pressure results in the transition zone. This can lead to the formation of bubbles, so that the quality of the conveyed material is not acceptable.
In order to be able to preclude this with certainty, it would be possible to increase the conveying rate of the extruder screw. However, there then results an overpressure in the transition zone, which stresses the construction and impairs the efficiency or output rate.
It is therefore an object of the present invention to provide an extruder arrangement of the aforementioned general type that provides an improved quality of the material that is to be extruded, whereby none-the-less an economical manufacture should be necessary.
This object is inventively realized by an extruder arrangement where the conveying device is in the form of a planetary pump, and wherein the planetary pump is provided with a rotatably mounted outer ring. Advantageous further developments can be found in the dependent claims.
The inventive approach permits, with surprisingly straightforward means, to keep the quality of the extruded material continuously uniform, even if different materials, for example on the one hand synthetic rubber mixtures and on the other hand mixtures of natural rubber, are utilized. A screw extruder conveys on the basis of the internal friction, and produces a drag flow along the extruder screw. In contrast, a planetary pump is a volumetric conveyor, so that here the conveying rate is considerably less dependent upon the viscosity of the material that is to be conveyed. Thus, the inventive approach also makes it possible to convey in a manner that is relatively independent of viscosity, whereby none-the-less a good efficiency can be achieved with the inventive planetary pump.
Due to the rotatable mounting of the outer ring of the planetary pump, the conveying rate of the planetary pump can to a large extent be set.
For example, the outer ring can be provided with a brake that is controllable. It is then merely necessary to have a drive motor for the extruder screw that can then also at the same time drive the central gear or the planetary carrier of the planetary pump. The setting or adjustment is effected such that even with the greatest viscosity of the material that is to be conveyed, the conveying rate of the planetary pump is still sufficient to prevent an overpressure on the input side of the planetary pump. In this state the brake is then activated, so that the outer ring does not, or nearly does not, rotate along.
If the viscosity is lower, the conveying rate through the extruder screw is also reduced, so that with the outer ring stationary, the planetary pump would have too high of a conveying rate and an underpressure would result in the transition zone. Pursuant to the present invention it is then possible for the outer ring to rotate somewhat. In so doing, the conveying rate of the planetary pump is reduced, so that again the same conveying rates exist between planetary pump and extruder screw.
The setting of the brake can either be prescribed on the basis of empirical values as a function of the viscosity of the material that is to be conveyed, or there is effected an automatic adaptation that is then based, for example, upon a pressure measurement in the transition zone between extruder screw and planetary pump.
With this embodiment, a control device is activated by the pressure sensor that is provided there, and in turn sets the force of the brake.
In a modified embodiment, it is also possible, instead of the brake, to use a separate drive motor that permits an even more sensitive adjustment.
The inventive approach makes it possible to realize a load-symmetrical conveyance. The helical gearing of the planetary pump, in other words also of the planetary pinions, permits a volumetric conveyance. The helical gearing can have any suitable angle, for example an angle of 10to 60 degrees, preferably somewhat greater than 20 degrees.
The planetary pump is self-cleaning, and can support the end of the screw. Due to the realization at the end of the screw, an economical manufacture is possible, and the occurrence of leakage streams through gears or pinions toward the outside, as with a gear pump, is not possible. As a consequence of the planetary pump, a good output can be realized, and there results a volumetric conveyance that is independent of the material to be conveyed. On the other hand, the inventive approach ensures that the planetary pump will always be supplied with material, so that it will also always convey.
Further advantages, details and features can be seen from the following description of one exemplary embodiment with the aid of the drawing.